Proton Residual Range Reconstruction and Impact on Dose to the Target Object in a Proton Imaging System Purpose: Proton radiography would be the most direct method of image guidance for proton therapy We aimed to develop a high-performance, low-cost proton radiography system based on wellestablished fast scintillator technology We also aimed to achieve the lower dose to the patient, relative to equivalent x-ray images, that is possible with proton imaging This dose advantage relies on a precise reconstruction of the residual ranges of individual protons traversing the patient, and a strategy to maintain low residual range during the scan Methodology: We have developed an algorithm to reconstruct proton residual range with our proton imaging system We tested this algorithm with simulated data, and compared simulated data with test beam data from our actual detector We also used simulations to understand the effect of residual range on dose to the patient Results: We find that for protons traversing 20 cm (water-equivalent) of material, our detector achieves a residual range resolution, for individual protons, dominated by the intrinsic range fluctuations through the material Therefore, as individual protons are averaged to form the image, the intrinsic fluctuations are the major factor in the total dose to the patient We also find that the dose to the patient is lower for lower residual ranges ProtonVDA Inc Stritch School of Medicine Loyola University - Chicago Northwestern Medicine Chicago Proton Center Time (sec) 0.12 E DeJongh, F DeJongh, V Rykalin J Welsh M Pankuch Northwestern: Scanning pencil beam at ultra-low intensity Transverse position from two position-weighted Range detector outputs • Range reconstruction uses total energy output as well as positionweighted outputs • Simulation: Uncertainty in residual range is dominated by intrinsic fluctuations through water • Plot shows one quadrant of 20x20x10 cm detector • Due to fluctuations in energy loss, the protons arrive at the detector with a range resolution of 2-2.5 mm • The intrinsic resolution from the water is approximately 2.5 mm • Perfect Detector: Resolution determined only by Intrinsic fluctuations through water Real 3.5 Calculation, for a fixed final residual range resolution in image: • Vertical axis: Relative dose to target object • Horizontal axis: Residual range 2.5 Relative dose • One dot = One proton • Time differences are quantized from RF accelerator system • Clusters around 0.06V are single proton events • Clusters at 0.12V are two-proton events • Clusters at 0.09V are from protons sitting on a tail of a proton 10 nsec earlier • Nuclear scatter events fall below 0.06V 1.5 Includes nuclear effects 0.5 Dependence of pulse height on range: Approximately linear (from a convolution of light yield with photon collection efficiency) 0.7 6.05 11.86 18.08 24.68 31.64 Residual Range (cm) Simulation of uncertainty on reconstruction of transverse position of track Determines final image sharpness www.postersession.com